The invention discloses a coating method for effectively inhibiting oxygen loss of a lithium-enriched magnesium-based positive electrode material and belongs to the field of positive electrode materials for lithium ion cells. The coating method comprises the following steps: 1) evenly dispersing a prepared lithium-enriched magnesium-based positive electrode material in deionized water or other organic solvents under ultrasonic waves; 2) dissolving molybdate and manganese salt in an organic solvent or deionized water to obtain a solution; 3) adding a molybdate solution and a manganese salt solution into dispersion liquid of a lithium-enriched material dropwise under the condition of a water batch, adjusting the pH of the solution, making the molybdate and the manganese salt react to generate manganese molybdate, and depositing the manganese molybdate on the surface of the lithium-enriched material in situ; and 4) calcining the filtered, washed and dried coating material at a temperatureof 450 to 600 DEG C for 4 to 6 hours, and cooling the material to room temperature to finally obtain an MnMoO4-coated lithium-enriched magnesium-based positive electrode material. According to the method, the surface of the lithium-enriched magnesium-based positive material is coated with MnMoO4 in situ through a depositing method. The coating method is simple in process and low in cost, can effectively inhibit the oxygen loss in the first cycle of charging and discharging and remarkably improve the coulombic efficiency and cycle performance of the material, and has a wide application prospect.